asim: add SetSimulationSettings as a mutation event

This commit adds SetSimulationSettings as a delayed mutation event, enabling
data-driven tests to modify simulation settings in the middle of the simulation.
Note that this is left unused as of now. This will support future changes like
updating the rebalance mode during a run.

Epic: none
Release note: none

Author: wenyihu6

pkg/kv/kvserver/asim/event/mutation_event.go

@@ -51,11 +51,19 @@ type SetNodeLocalityEvent struct {
 	LocalityString string
 }
 
+// SetSimulationSettingsEvent represents a mutation event responsible for
+// changing a simulation setting during the simulation.
+type SetSimulationSettingsEvent struct {
+	Key   string
+	Value interface{}
+}
+
 var _ Event = &SetSpanConfigEvent{}
 var _ Event = &AddNodeEvent{}
 var _ Event = &SetNodeLivenessEvent{}
 var _ Event = &SetCapacityOverrideEvent{}
 var _ Event = &SetNodeLocalityEvent{}
+var _ Event = &SetSimulationSettingsEvent{}
 
 func (se SetSpanConfigEvent) Func() EventFunc {
 	return MutationFunc(func(ctx context.Context, s state.State) {
@@ -129,3 +137,13 @@ func (sne SetNodeLocalityEvent) Func() EventFunc {
 func (sne SetNodeLocalityEvent) String() string {
 	return fmt.Sprintf("set node locality event with nodeID=%d, locality=%v", sne.NodeID, sne.LocalityString)
 }
+
+func (se SetSimulationSettingsEvent) Func() EventFunc {
+	return MutationFunc(func(ctx context.Context, s state.State) {
+		s.SetSimulationSettings(se.Key, se.Value)
+	})
+}
+
+func (se SetSimulationSettingsEvent) String() string {
+	return fmt.Sprintf("set simulation settings event with key=%s, value=%v", se.Key, se.Value)
+}

pkg/kv/kvserver/asim/state/impl.go

@@ -11,6 +11,7 @@ import (
 	"context"
 	"fmt"
 	"math"
+	"reflect"
 	"slices"
 	"sort"
 	"strconv"
@@ -1319,6 +1320,27 @@ func (s *state) RegisterConfigChangeListener(listener ConfigChangeListener) {
 	s.configChangeListeners = append(s.configChangeListeners, listener)
 }
 
+// SetSimulationSettings sets the simulation setting for the given key to the
+// given value.
+func (s *state) SetSimulationSettings(Key string, Value interface{}) {
+	settingsValue := reflect.ValueOf(s.settings).Elem()
+	settingsType := settingsValue.Type()
+
+	for i := 0; i < settingsValue.NumField(); i++ {
+		field := settingsType.Field(i)
+		if field.Name == Key {
+			fieldValue := settingsValue.Field(i)
+			if fieldValue.CanSet() {
+				newValue := reflect.ValueOf(Value)
+				if newValue.Type().ConvertibleTo(fieldValue.Type()) {
+					fieldValue.Set(newValue.Convert(fieldValue.Type()))
+				}
+			}
+			break
+		}
+	}
+}
+
 // node is an implementation of the Node interface.
 type node struct {
 	nodeID NodeID

pkg/kv/kvserver/asim/state/state.go

@@ -197,6 +197,8 @@ type State interface {
 	// RegisterConfigChangeListener registers a listener which will be called
 	// when a cluster configuration change occurs such as a store being added.
 	RegisterConfigChangeListener(ConfigChangeListener)
+	// SetSimulationSettings sets the simulation settings for the state.
+	SetSimulationSettings(Key string, Value interface{})
 }
 
 // Node is a container for stores and is part of a cluster.